Such feedthroughs typically have a flange, through use of which they are inserted into a housing wall of the electro-medical implant, preferably by a thermal joining method such as welding or soldering. An apparatus having, inter alia, a circuit board which is capable of processing or transmitting electrical signals, is located in the housing. The feedthrough has at least one feedthrough bushing, a flange enclosing the at least one feedthrough bushing, in which at least one terminal pin is seated, which is enclosed by the at least one feedthrough bushing. The terminal pin extends through the flange and the feedthrough bushing from an inner end in the interior of the housing to an outer end, which lies outside the hermetically sealed housing. The terminal pin is typically connected to the at least one feedthrough bushing and/or the at least one feedthrough bushing is typically connected to the flange using a soldered connection, preferably using a gold solder if metal coated feedthrough bushings are used, or using a biocompatible glass solder (type 8625 from Schott) if uncoated feedthrough bushings are used. In consideration of the fact that the outer end of the terminal electrode can come into contact with the body tissue surrounding the implant in a medical implant, the terminal pins are typically manufactured from a biocompatible material, such as, but not limited to, niobium (Nb), platinum (Pt), iridium (Ir), platinum/iridium alloys (Pt/Ir), tantalum (Ta), titanium (Ti), zirconium (Zr), hafnium (Hf), medical stainless steel (e.g., 316L), or alloys made of these materials. FeNi, FeNiCo, FeCr, molybdenum (Mo), tungsten (W), chromium (Cr), FeCr, vanadium (V), aluminum (Al), or other alloys made of these materials are also possible as materials for the terminal pin. It will be apparent to one of ordinary skill in the art that other materials and alloys have similar properties may be utilized for the terminal pins without departing from the spirit and scope of the present invention.
The feedthrough bushing is typically produced from a ceramic material, such as aluminum oxide (Al2O3). Above all in the case of terminal pins made of niobium, tantalum, or titanium, the problem exists that only welding methods come into consideration in order to produce a connection to other conductors, for example, to the terminal lines or to device electronics attached to the circuit in the interior of the implant, for the production of secure, low-resistance, mechanically stable, and long-lived electrical contacts to the described biocompatible terminal pins. The required high temperatures of the welding procedure may generate metal vapors and/or welding sprays, however, which impair the electrical insulation capability of the ceramics and/or damage the circuit boards and therefore frequently require additional protective measures. Due to these properties, reflow soldering, which is well known in the electronics sector, has simple production technology, and is efficient, is also not possible or is not readily usable with such a terminal pin.
In the case of the described ceramic feedthroughs having platinum/iridium terminal pins, it is known that without special protective precautions, they display problems with the detachment of the metal coating of the feedthrough bushings upon the soldering using gold solder and have poor wettability of the platinum/iridium surfaces with soft solder. As a result, the noted reflow soldering is generally unreliable.
Fundamentally, the coating of the pin surfaces in the case of niobium, tantalum, or titanium terminal pins on the inner side for easy wettability with soft solder for the attachment to the internal electronics is either not possible at all or is only possible with increased effort, in that metal coatings which can be soft soldered are applied using welding technology or plasma-physical pathways, for example. Surfaces or coatings which can be soft soldered on nickel, tantalum, or titanium, which are applied with the aid of fluxes or using electroplating, have been unknown up to this point.
A feedthrough for implantable medical devices having an integrated capacitive filter is known from U.S. Pat. No. 5,870,272, in which the electrical contacting and mechanical connection between a pin comprising niobium, for example, and an inner contact circuit with the capacitive filter interposed is produced via a complex, multistep soldering configuration using hard and soft solders. This design is too complex for feedthroughs having simple terminal electrodes, and efficient manufacturing would not be possible in the case of a corresponding layout of the feedthrough.
The present invention is directed toward overcoming one or more of the above-identified problems.